Interfacial oxygen-scavenging-driven formation of atomic-layer-deposited MoO2 on MoNx electrodes for improved TiO2 capacitor performance

Abstract

For highly scaled dynamic random access memory (DRAM) capacitors, metastable MoO₂ has been proposed as a promising electrode due to its superior properties such as high work function and excellent interface characteristics with rutile TiO₂. In this study, a novel method to fabricate MoO₂ electrodes was developed using atomic layer deposition (ALD). ALD MoO_x films were deposited using bis(tert-butylimido)-bis(dimethylamido)molybdenum and O₃ as the Mo precursor and oxidant, respectively. While MoO_x films grown on SiO₂ substrates exhibited mixed phases of MoO₃ and Mo₄O₁₁, those deposited on MoN_x substrates transformed into metastable monoclinic MoO₂ after annealing at 500 °C. This phase transition was enabled by the strong oxygen-scavenging effect of the underlying MoN_x layer, which promoted the formation of molybdenum suboxide with a reduced Mo : O ratio. Based on this approach, RuO₂/TiO₂ (or Al-doped TiO₂)/MoO₂/MoN_x capacitor stacks were fabricated. The TiO₂ and Al-doped TiO₂ layers formed high-quality rutile phases with dielectric constants of 157 and 124, respectively, due to local epitaxial growth on MoO₂. Moreover, the MoO₂/MoN_x electrode significantly reduced leakage current compared to MoN_x-only electrodes. The Al-doped TiO₂ capacitor demonstrated the best performance, achieving a leakage current density of 6.7 × 10⁻⁷ A cm⁻² at 0.8 V and an equivalent oxide thickness of 0.37 nm.